Keygen - A dead-simple software licensing API built for developers
Quick License Manager - Quick License Manager (QLM) is a license protection framework that creates professional and secure license keys to protect software against piracy.
Labs64 NetLicensing - Monetize your digital products and services
SoftwareKey Licensing System - SoftwareKey System is a set of software development tools that help programmers implement copy protection, license activation and management, metering, eCommerce, and business automation.
LicenseSpring - Reliable and easy to use License-As-A-Service (LaaS) for for any software application
CodeMeter - License Management